The present invention relates to a method providing the means for recognizing the origin and/or the content of an RF signal.
Many techniques are known for combating the scrambling of signals such as those of radars. However, in a field such as that of the reception of radiolocation signals, it is necessary to have measures (called pseudomeasures) provided by satellites and ephemeride data. It is relatively easy to protect the ephemeride data in order to guarantee the origin and/or the content thereof. On the other hand, the characteristics of the measurement signals are in the public domain and can therefore not be protected. It is therefore easy to emulate these signals for a user to obtain false geographic position coordinates. The same applies in other fields of digital transmissions such as telecommunications or television programs broadcasts.
Little research has been carried out in order to guarantee the origin of such RF signals. Specifically, it is now possible, if sufficiently powerful computers are used, to produce in an ill-intentioned way signals imitating those transmitted by the geolocation satellites. These deception techniques are called “spoofing”.
A few indications in order to try to authenticate the received signals have been described for example in an article by Logan SCOTT “Anti-Spoofing and Authenticated Signal Architectures for Civil Navigation systems” that appeared in the review ION GPS/GNSS 2003, 9-12 Sep. 2003, Portland, Oreg. However, determining the origin and/or the content of the received signals also requires considerable computation means consuming no small amount of power and is therefore not within the scope of a simple user of a radionavigation receiver or of an ordinary user subscribed to digital television programs.